Did you know that the sago palm (Cycas revoluta) isn’t a true palm but a cycad, an ancient plant family related to conifers?
Native to subtropical Japan, its arching fronds bring an exotic flavour indoors. Though the plant is mostly easy to care for, it can be prone to yellow spotting on the leaves.
There are a few reasons a sago palm can develop yellow spots. Usually, it’ll be down to a cycad aulacaspis scale infestation or a mineral deficiency – most commonly magnesium or manganese. Let’s find out how to diagnose the cause and treat it.
Why does your sago palm have yellow spots?
It’s most likely your suffering sago has yellow leaf spots because of cycad scale insects or a lack of magnesium or manganese.
Either way, it’s easily fixed and can be treated with affordable and easily accessible solutions. A little detective work should help you pin down which one.
1. Cycad aulacaspis scale infestation
The cycad aulacaspis scale is an armour plated sucking bug that feeds off the sago palm. If your sago is afflicted, you may see a white dusting of what looks like snow on the fronds of your plant – but they’re bugs!
Newly hatched scale invades the trunk and base of the leaves. They then continue to spread out into the outer leaves as well as the seeds and roots of the sago.
Sucking the sap out of the plant, scale insects leave damaged yellow spots on the foliage after feeding.
Scales are a pest that can be found all year round. However, their population grows as the temperature rises, so your plant is most likely to be affected in summer.
How to treat a cycad aulacaspis scale infestation
If found early a scale infestation can be treated quite easily. Left unchecked, the scale can overrun the plant and cause it to die.
To treat a scale infestation all you need to do is follow these steps:
- Spray the plant vigorously with water, removing any dead or living scales.
- Apply a good horticultural oil or bug spray once a week for a month.
- If the leaves of the plant are heavily infested, remove them before starting treatment and dispose of them well away from your plant.
2. Manganese deficiency
If you can’t see any sign of scale bugs on your sago palm’s leaves, it’s time to address any nutrient deficiencies.
As a sago isn’t a true palm, it won’t respond very well to a general palm fertilizer. You could opt for a specialist sago fertilizer that contains a good variety of nutrients and micronutrients.
However, to treat a specific issue like yellow spots, it’s a good idea to treat your plant with specific minerals. Not only can it correct problems more quickly, it gives you a better understanding of your plant and its needs.
Manganese is vital for plant growth. A key component in the development of chloroplasts, manganese is also important for the production of enzymes, as well as respiration and photosynthesis.
A lack of manganese is common in soil with a neutral or high pH or in soils composed mostly of calcium carbonate.
How to treat a manganese deficiency
A manganese deficiency can be treated with manganese sulphate. This is widely available online and can be applied into the soil or directly onto the plant as a spray.
QUICK NOTE – manganese sulphate should not be confused with magnesium sulphate (Epsom salts), which are used to treat a magnesium deficiency.
3. Magnesium deficiency
Magnesium is another mineral essential for plant growth. It’s a key element in the chlorophyll molecule, the powerhouse of the leaf where photosynthesis occurs. This is where the signature green colour of a plant’s leaves comes from.
Magnesium also plays a pivotal role in a plant’s ability to absorb other minerals and elements including nitrogen and phosphorus.
A magnesium deficiency is most common in light soils with little organic matter. As a water-soluble molecule, magnesium is easily leached from soil through watering.
A magnesium deficiency could therefore be a sign that you are overwatering your plant.
How to treat a magnesium deficiency
Sago palms prefer dry soil to wet soil, and only need watering once the surface of the soil is dry. Twice a week in summer and every 7-10 days in winter is usually enough.
Scale back on the amount you are watering your sago if you have been watering more frequently. If you don’t think overwatering is the issue, a magnesium deficiency can be easily resolved with a magnesium rich fertilizer or Epsom salts (magnesium sulphate).
For the most effective form of absorption, dilute the Epsom salts in water and use as a foliar spray.
How to tell if your sago palm needs magnesium or manganese
There are a lot of similarities between magnesium and manganese deficiencies. Both cause yellow spots. Both are fixed using similar solutions. Both even sound similar!
To decide whether your sago palm needs magnesium or manganese, notice where the yellow spots occur first.
A magnesium deficiency will cause yellowing on the older leaves first. These are the leaves found nearer the bottom of the plant.
In contrast, manganese is less mobile in the plant, so symptoms of a deficiency will show on younger leaves first. These are found closer to the stem of the plant.
Stop your sago getting yellow spots again
Now you know the different causes of the yellow spots and how to treat them, how do you stop them from coming back again?
Simple – keep your plant healthy! It’s the most reliable prevention method possible.
Make sure your plant is in partial shade; full exposure to the sun at all times can be damaging. Maintain a moist, well-drained soil by making sure you don’t under or overwater the plant.
And don’t forget to feed your plant during the growing season to ensure it is getting all the nutrients it needs. Choose a specialist sago fertilizer that contains a good mix of micronutrients alongside nitrogen and potassium.
Over to you
Hope this helps you tackle those yellow spots that have sprung up on your sago palm. Most solutions are affordable and take little effort other than a quick visit to your local garden centre.
Once your sago has recovered, giving it adequate light, heat, water and nutrients should help it live a long and healthy life – free from those pesky yellow spots!